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Lewis acid-catalyzed regiospecific opening of vinyl epoxides by alcohols
TETRAHEDRON LETTERS Pergamon
Tetrahedron Letters 41 (2000) 3829–3831
Lewis acid-catalyzed regiospecific opening of vinyl epoxides by alcohols Guillaume Prestat,a Christophe Baylon,a Marie-Pierre Heck a,∗ and Charles Mioskowski a,b,∗ a
CEA-CE Saclay, Service des Molécules Marquées, Bât 547, Département de Biologie Cellulaire et Moléculaire, F-91191 Gif sur Yvette cedex, France b Laboratoire de Synthèse Bio-organique associé au CNRS, Faculté de Pharmacie, Université Louis Pasteur, 74 route du Rhin BP24, F-67401 Illkirch, France Received 17 February 2000; accepted 18 March 2000
Abstract A Lewis acid-catalyzed, regiospecific opening of vinyl epoxides to β-hydroxy allyl-ethers was performed using equimolar quantities of both alcohols and oxiranes. BF3 ·Et2 O proved to be the most efficient catalyst for various substituted alcohols. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: vinyl epoxide; alcohol; ring-opening; Lewis acid.
In the course of our investigations of the synthesis of natural and non-natural Annonaceous acetogenins, we were interested in the nucleophilic ring-opening of vinyl epoxides with 1 molar equivalent of alcohol (Scheme 1).
Scheme 1.
Despite the rich literature on the chemistry of epoxide opening,1 to the best of our knowledge there are few reports concerning ring-opening of vinyl epoxides by alcohols.2–4 Nicolaou et al. demonstrated the CSA (camphorsulfonic acid)-catalyzed intramolecular ring-opening of vinyl epoxides.2 Posner and Rogers reported the alumina-promoted opening of 1,3-cyclopentadiene monoxide with a large excess of allylic alcohol.3 A palladium(II)-catalyzed ring-opening of vinyl epoxide with cyclic stannyl diether has also been described by Trost and Teneglia.4 These last two examples are the only reported intermolecular reactions to date, and are limited to cyclic compounds3 or require elaborate reagents.4 Furthermore, general methods for the opening of non-vinylic epoxides with oxygen nucleophiles were ∗
Corresponding author. E-mail: [email protected] (M.-P. Heck), [email protected] (C. Mioskowski)
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. P I I: S0040-4039(00)00496-2
tetl 16775
3830
usually performed with alcohol used in large excess or as solvent.5 These features limit the synthetic utility of this reaction. Here we present our results of a Lewis acid-mediated regiospecific opening of vinyl epoxides using equal amounts of alcohol and oxirane, leading to β-hydroxy allyl-ethers. 3,4-Epoxy-tridec-1-ene 1, chosen as a model reagent, was prepared in a 60:40 cis:trans mixture from decylaldehyde and allyl arsonium ylide according to a known procedure.6 Oxirane 1 was allowed to react with 1 equivalent of various types of alcohols (2a–2e) as shown in Scheme 2. Reactions were carried out at room temperature in methylene chloride (1 M) in the presence of different catalysts.
Scheme 2.
The ring-opening of 1 was first attempted with 3,4-dimethoxybenzyl alcohol 2a. The reaction was very slow when using Nicolaou’s intramolecular conditions (CSA 10% mol) and afforded 3a in only a moderate yield (35% after 15 days). Similar results were obtained employing other organic acids such as PPTS (pyridinium-p-toluenesulfonate) or pTsOH. Either basic conditions (sodium alcoholate of 2a) or LiClO4 catalysis led to complete recovery of starting materials. We then turned our attention to the use of Lewis acids. Catalytic amounts of MgBr2 , Et2 AlCl2 , Me2 AlCl2 , Ti(OiPr)4 and TiCl2 (OiPr)2 gave a rapid and complete degradation of the vinyl epoxide. Other Lewis acid catalysts proved successful (Table 1). Tin, titanium and zinc chlorides afforded the opened product 3a in moderate yields (respectively, 15, 18 and 35%). Trimethylsilyl, tin, copper and iminium triflates generated the desired product in 55–73% yields. The use of BF3 ·Et2 O gave the best result: 3a was isolated in a 76% yield using only 1% mol of catalyst after 30 min of stirring. BF3 ·Et2 O was selected (1% mol, 30 min) for the study of alcohols 2b–2e. Yields were good with activated (2b, 75%), linear (2c, 73%) and hindered (2d, 70%) alcohols. Nucleophilic ring-opening even occurred in 52% yield with the deactivated alcohol 2e. The reaction yield was not significantly affected by changing the solvent (C6 H6 , Et2 O) and/or by varying the temperature (−78°C to reflux). In contrast, lowering the concentration from 1 to 0.1 M resulted in a lowering in yield (76 to 30% for 3a). In all the reported examples the ring-opening reaction appeared to be regiospecific. Only nucleophilic attack at the C-3 position of the vinyl epoxide was observed (Scheme 2). It should be noted that β-hydroxy allyl-ethers were isolated as a 60:40 diastereomeric mixture similar to the cis:trans ratio of starting epoxide 1. The only by-products resulted from the degradation of vinyl epoxide.7 In summary, we have presented the first preparative synthesis of β-hydroxy allyl-ethers by condensation of alcohols on a vinyl epoxide using equimolar quantities of both partners. The reaction was catalyzed by BF3 ·Et2 O (1% mol) in methylene chloride (1 M) at room temperature. The mild conditions
3831 Table 1 Catalyzed ring-opening reaction of vinyl epoxide 1 (1 equiv.) with alcohols 2a–e (1 equiv.)
and easy work-up of this opening reaction allow its application to sensitive substrates as reported in the following paper,8 where this methodology is used as a key step in the enantiospecific synthesis of (−)-muricatacin. Experimental procedure: A 10% solution of BF3 ·Et2 O (12 µL, 0.01 mmol) in CH2 Cl2 was added dropwise to a mixture of 1 (1 mmol) and 2a–2e (1 mmol) in CH2 Cl2 (2 mL). The reaction was stirred for 30 min at room temperature and then concentrated under reduced pressure. The residue was purified by SiO2 chromatography to yield β-hydroxy allyl-ether. Acknowledgements Financial support was provided in part by the Commissariat à l’Energie Atomique (fellowships for G.P. and C.B.). References 1. (a) Mitsunobu, O. In Comprehensive Organic Synthesis; Trost, B. M.; Fleming, L.; Pattenden, G., Eds.; Pergamon Press: Oxford, 1990; Vol. 6, pp. 88–93. (b) Birkinshaw, T. N. In Comprehensive Organic Functional Group Transformations; Katrisky, A. R.; Meth-Cohn, O.; Rees, C. W.; Roberts, S. M., Eds.; Pergamon Press: Oxford, 1990; Vol. 1, pp. 204–220. 2. (a) Nicolaou, K. C.; Duggan, M. E.; Hwang, C.-K.; Somers, P. K. J. Chem. Soc., Chem. Commun. 1985, 1359–1362. (b) Nicolaou, K. C.; Prasad, C. V. C.; Somers, P. K.; Hwang, C.-K. J. Am. Chem. Soc. 1989, 111, 5330–5334. (c) Nicolaou, K. C.; Duggan, M. E.; Hwang, C.-K. J. Am. Chem. Soc. 1989, 111, 6676–6682. 3. Posner, G. H.; Rogers, D. Z. J. Am. Chem. Soc. 1977, 99, 8214–8218. 4. Trost, B. M.; Tenaglia, A. Tetrahedron Lett. 1988, 29, 2931–2934. 5. (a) Otera, J.; Yoshinaga, Y.; Hirakawa, K. Tetrahedron Lett. 1985, 26, 3219–3222. (b) Iranpoor, N.; Mohammadpour Baltork, I. Tetrahedron Lett. 1990, 31, 735–738. 6. Ousset, J. B.; Mioskowski, C.; Solladié, G. Tetrahedron Lett. 1983, 24, 4419–4422. 7. Degradation of vinyl epoxide in the presence of a catalytic quantity of Lewis acid also occurred in the absence of alcohol. 8. Baylon, C.; Prestat, G.; Heck, M.-P.; Mioskowski, C. Tetrahedron Lett. 2000, 41, 3833–3835.
Tetrahedron Letters 41 (2000) 3829–3831
Lewis acid-catalyzed regiospecific opening of vinyl epoxides by alcohols Guillaume Prestat,a Christophe Baylon,a Marie-Pierre Heck a,∗ and Charles Mioskowski a,b,∗ a
CEA-CE Saclay, Service des Molécules Marquées, Bât 547, Département de Biologie Cellulaire et Moléculaire, F-91191 Gif sur Yvette cedex, France b Laboratoire de Synthèse Bio-organique associé au CNRS, Faculté de Pharmacie, Université Louis Pasteur, 74 route du Rhin BP24, F-67401 Illkirch, France Received 17 February 2000; accepted 18 March 2000
Abstract A Lewis acid-catalyzed, regiospecific opening of vinyl epoxides to β-hydroxy allyl-ethers was performed using equimolar quantities of both alcohols and oxiranes. BF3 ·Et2 O proved to be the most efficient catalyst for various substituted alcohols. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: vinyl epoxide; alcohol; ring-opening; Lewis acid.
In the course of our investigations of the synthesis of natural and non-natural Annonaceous acetogenins, we were interested in the nucleophilic ring-opening of vinyl epoxides with 1 molar equivalent of alcohol (Scheme 1).
Scheme 1.
Despite the rich literature on the chemistry of epoxide opening,1 to the best of our knowledge there are few reports concerning ring-opening of vinyl epoxides by alcohols.2–4 Nicolaou et al. demonstrated the CSA (camphorsulfonic acid)-catalyzed intramolecular ring-opening of vinyl epoxides.2 Posner and Rogers reported the alumina-promoted opening of 1,3-cyclopentadiene monoxide with a large excess of allylic alcohol.3 A palladium(II)-catalyzed ring-opening of vinyl epoxide with cyclic stannyl diether has also been described by Trost and Teneglia.4 These last two examples are the only reported intermolecular reactions to date, and are limited to cyclic compounds3 or require elaborate reagents.4 Furthermore, general methods for the opening of non-vinylic epoxides with oxygen nucleophiles were ∗
Corresponding author. E-mail: [email protected] (M.-P. Heck), [email protected] (C. Mioskowski)
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. P I I: S0040-4039(00)00496-2
tetl 16775
3830
usually performed with alcohol used in large excess or as solvent.5 These features limit the synthetic utility of this reaction. Here we present our results of a Lewis acid-mediated regiospecific opening of vinyl epoxides using equal amounts of alcohol and oxirane, leading to β-hydroxy allyl-ethers. 3,4-Epoxy-tridec-1-ene 1, chosen as a model reagent, was prepared in a 60:40 cis:trans mixture from decylaldehyde and allyl arsonium ylide according to a known procedure.6 Oxirane 1 was allowed to react with 1 equivalent of various types of alcohols (2a–2e) as shown in Scheme 2. Reactions were carried out at room temperature in methylene chloride (1 M) in the presence of different catalysts.
Scheme 2.
The ring-opening of 1 was first attempted with 3,4-dimethoxybenzyl alcohol 2a. The reaction was very slow when using Nicolaou’s intramolecular conditions (CSA 10% mol) and afforded 3a in only a moderate yield (35% after 15 days). Similar results were obtained employing other organic acids such as PPTS (pyridinium-p-toluenesulfonate) or pTsOH. Either basic conditions (sodium alcoholate of 2a) or LiClO4 catalysis led to complete recovery of starting materials. We then turned our attention to the use of Lewis acids. Catalytic amounts of MgBr2 , Et2 AlCl2 , Me2 AlCl2 , Ti(OiPr)4 and TiCl2 (OiPr)2 gave a rapid and complete degradation of the vinyl epoxide. Other Lewis acid catalysts proved successful (Table 1). Tin, titanium and zinc chlorides afforded the opened product 3a in moderate yields (respectively, 15, 18 and 35%). Trimethylsilyl, tin, copper and iminium triflates generated the desired product in 55–73% yields. The use of BF3 ·Et2 O gave the best result: 3a was isolated in a 76% yield using only 1% mol of catalyst after 30 min of stirring. BF3 ·Et2 O was selected (1% mol, 30 min) for the study of alcohols 2b–2e. Yields were good with activated (2b, 75%), linear (2c, 73%) and hindered (2d, 70%) alcohols. Nucleophilic ring-opening even occurred in 52% yield with the deactivated alcohol 2e. The reaction yield was not significantly affected by changing the solvent (C6 H6 , Et2 O) and/or by varying the temperature (−78°C to reflux). In contrast, lowering the concentration from 1 to 0.1 M resulted in a lowering in yield (76 to 30% for 3a). In all the reported examples the ring-opening reaction appeared to be regiospecific. Only nucleophilic attack at the C-3 position of the vinyl epoxide was observed (Scheme 2). It should be noted that β-hydroxy allyl-ethers were isolated as a 60:40 diastereomeric mixture similar to the cis:trans ratio of starting epoxide 1. The only by-products resulted from the degradation of vinyl epoxide.7 In summary, we have presented the first preparative synthesis of β-hydroxy allyl-ethers by condensation of alcohols on a vinyl epoxide using equimolar quantities of both partners. The reaction was catalyzed by BF3 ·Et2 O (1% mol) in methylene chloride (1 M) at room temperature. The mild conditions
3831 Table 1 Catalyzed ring-opening reaction of vinyl epoxide 1 (1 equiv.) with alcohols 2a–e (1 equiv.)
and easy work-up of this opening reaction allow its application to sensitive substrates as reported in the following paper,8 where this methodology is used as a key step in the enantiospecific synthesis of (−)-muricatacin. Experimental procedure: A 10% solution of BF3 ·Et2 O (12 µL, 0.01 mmol) in CH2 Cl2 was added dropwise to a mixture of 1 (1 mmol) and 2a–2e (1 mmol) in CH2 Cl2 (2 mL). The reaction was stirred for 30 min at room temperature and then concentrated under reduced pressure. The residue was purified by SiO2 chromatography to yield β-hydroxy allyl-ether. Acknowledgements Financial support was provided in part by the Commissariat à l’Energie Atomique (fellowships for G.P. and C.B.). References 1. (a) Mitsunobu, O. In Comprehensive Organic Synthesis; Trost, B. M.; Fleming, L.; Pattenden, G., Eds.; Pergamon Press: Oxford, 1990; Vol. 6, pp. 88–93. (b) Birkinshaw, T. N. In Comprehensive Organic Functional Group Transformations; Katrisky, A. R.; Meth-Cohn, O.; Rees, C. W.; Roberts, S. M., Eds.; Pergamon Press: Oxford, 1990; Vol. 1, pp. 204–220. 2. (a) Nicolaou, K. C.; Duggan, M. E.; Hwang, C.-K.; Somers, P. K. J. Chem. Soc., Chem. Commun. 1985, 1359–1362. (b) Nicolaou, K. C.; Prasad, C. V. C.; Somers, P. K.; Hwang, C.-K. J. Am. Chem. Soc. 1989, 111, 5330–5334. (c) Nicolaou, K. C.; Duggan, M. E.; Hwang, C.-K. J. Am. Chem. Soc. 1989, 111, 6676–6682. 3. Posner, G. H.; Rogers, D. Z. J. Am. Chem. Soc. 1977, 99, 8214–8218. 4. Trost, B. M.; Tenaglia, A. Tetrahedron Lett. 1988, 29, 2931–2934. 5. (a) Otera, J.; Yoshinaga, Y.; Hirakawa, K. Tetrahedron Lett. 1985, 26, 3219–3222. (b) Iranpoor, N.; Mohammadpour Baltork, I. Tetrahedron Lett. 1990, 31, 735–738. 6. Ousset, J. B.; Mioskowski, C.; Solladié, G. Tetrahedron Lett. 1983, 24, 4419–4422. 7. Degradation of vinyl epoxide in the presence of a catalytic quantity of Lewis acid also occurred in the absence of alcohol. 8. Baylon, C.; Prestat, G.; Heck, M.-P.; Mioskowski, C. Tetrahedron Lett. 2000, 41, 3833–3835.